The chironomid larvae of a small chalk stream in Berkshire, England

Abstract. 1. The longitudinal distributions of larval Chironomidae (Diptera) were examined for 1 year in the intermittent and perennial sections of the Winterbourne, a small chalk stream in Berkshire, England.
2. Forty-nine chironomid taxa were recorded at ten major sites which were sampled on six occasions and four additional taxa were recorded at sites sampled only once.
3. Cluster analyses using data from the major sampling sites identified three groups of sites. A pond in the stream channel which had a distinct chironomid fauna was distinguished from all other sites before the remaining intermittent sites were separated from all perennial sites on the basis of the chironomid fauna.
4. In the perennial stream, a site heavily shaded by trees had low species richness compared with partially and unshaded sites further downstream. The lowest site, which was near to the confluence with a larger chalk stream, the River Lambourn, had the highest number of taxa (thirty-five), including several which were frequent in the Lambourn.
5. By recording the occurrence of prepupae, an indication of emergence periods was obtained and many taxa were shown to have extended periods of emergence.